1. Field of the invention:
This invention relates to a process for producing blood powder by the continuous and automatic drying of the blood discharged from a slaughtered animal. The blood powder consists mainly of the coagulated and dried product of the proteins existing in the serum, but also contains cruor consisting of coagulated fibrin.
2. Description of the Prior Art:
Blood powder consists essentially of a good protein, and has been considered as providing an important assorted feed or compound fertilizer. Blood is, however, liable to decomposition far more quickly than other proteins, and the decomposed blood sends off an objectionable smell during the production of blood powder. Extensive facilities are required for preventing the scattering of any such smell. Moreover, as blood contains a lot of water, its drying requires a lot of time and a lot of fuel. This necessarily raises the cost of production of blood powder. Therefore, the current production of blood powder is greatly limited, and does not occupy more than 0.1% of the total assorted feed production. The majority of the slaughterhouses dispose of blood by activated sludge treatment with waste water. If it is possible to separate blood from any such sludge and utilize it, the load on an activated sludge system will be reduced to about one-third. This means a drastic reduction in the cost of equipment and operation.
The drying of blood for producing blood powder has hitherto been carried out by vacuum or spray heating. The conventional vacuum drying system does, however, not start heating until a certain quantity of blood is collected in a vessel. There is every likelihood that blood may be decomposed and send off an objectionable smell before the system is placed in operation.
According to the conventional spray drying system, blood is sprayed down from a height of about 10 m, and hot air is horizontally blown against the blood. It is, however, difficult to blow hot air uniformly against blood, and a part of blood which is not completely dried is decomposed and sends off an objectionable smell. The system is so large that it is very expensive to shield the whole system completely from its environment. The system also has a number of control problems, including the burning of blood by overheated air.
U.S. Pat. No. 3,615,651 discloses gelatinizing blood from which about 50 or 60 percent of water content has been vaporised through the injection of live steam. Also, U.S. Pat. No. 4,219,586 teaches an auger press by which at least 50% of the moisture from the gelatinous mass of blood is squeezed during the latter stage of augering and subsequent to gelatinizing.
However, extremely dry blood powder of good and uniform quality is not obtained without finding a solution to the below-mentioned problem. It is well known that blood plasma contains not only serum but also fibrinogen. The fibrinogen is exposed in air, so that it coagulates as a network of insoluble fibrin and forms the outer surface of a lump, with water content enclosed therein. This bio-phenomenon originally occurs to prevent the flow of blood from a wound in the living body.
The bio-phenomenon of fibrin also occurs during dehydrating work, with water content being enclosed into the lump made from the fibrin, by which sufficient dehydration is prevented or impeded.
It is considered to heat at a high temperature the lump enclosing water therewithin, in order to remove the water therefrom. However, upon heating the lump enclosing water at the high temperature, saccharide and soluble protein in the serum exude to the outer surface of the lump, and are concentrated. As the concentrated liquid has very strong adhesive properties, the lumps tend to adhere together to form a number of larger lumps. As such, the overall outer surface area of the lumps is reduced, and the drying of the blood is prevented or hampered.